An oil boiler, or burner, nozzle sprays heating oil into the unit's combustion chamber. It creates a pattern with the right shape and size to suit the shape of the chamber, and it yields a fine spray so the oil burns as efficiently as possible.
Oil boiler nozzles have a brass exterior with a stainless steel insert in the center. The use of stainless steel in the center minimizes the wear and tear caused by the hot oil. When the whole unit was made of brass, the opening of the nozzle would deteriorate during the cold season, causing a faulty spray pattern.